PORT-AU-PRINCE , Haiti -LRB- CNN -RRB- -- At least 50 people have died in a school collapse in in Petionville , near the Haitian capital of Port-au-Prince , officials said Friday night .

Haitians try to help victims at a school that collapsed Friday in Petionville , near Port-au-Prince .

Rescue personnel planned to continue working into the night to dig out students and teachers buried in the rubble , the Red Cross said .

At least 100 people have been injured , the Haitian Civil Protection Bureau said . The death toll is expected to rise .

Officials said the school could have held as many as 700 people when the collapse occurred at 10 a.m. -LRB- 10 a.m. ET -RRB- Some students were in class while others were in a playground , Haitian media reported .

`` We are looking at major casualties here , '' Claudon said .

He said dozens of students appeared to be trapped inside but could n't give an exact number . However , he said it was a typical school day and the building had been crowded .

Most of the students at the College La Promesse Evangelique range in age from 10 to 20 , he said , but there are younger ones as well . Haitian press reports said the school has kindergarten , primary and secondary students .

President Rene Preval and Prime Minister Michele Pierre-Louis toured the disaster area .

`` I heard and saw with my own eyes children appealing for help , '' Preval was quoted as saying on the French language www.haitipressnetwork.com .

`` We are taking all necessary steps , '' Pierre-Louis said . '' The government has mobilized to save those who can be saved . ''

Preval asked residents to stay away from the area so police and rescue officials could do their work unimpeded .

Michaele Gedeon , president of Haiti 's Red Cross , said she heard the voices of distraught children as rescuers tried to calm them while she was on the phone attempting to coordinate emergency rescue efforts . Watch as the Red Cross official describes the scene ''

`` On the phone , you can hear so many children , you know , crying , crying and saying , ` this one is dead , ' ` that one is dead , ' '' she said .

Claudon said hundreds of bystanders and rescue workers were digging through the rubble , but `` what we need right now is heavy search-and-rescue equipment . ''

Claudon later said , `` local authorities are doing their best . ''

Fifty to 60 patients , 30 of them severely injured , were taken to Trinite Hospital in Port-au-Prince , said Isabelle Mouniaman Nara , the head of mission in the capital for Medecins sans Frontieres .

Another 150 patients were treated elsewhere , Nara said Friday night .

The situation at Trinite `` is under control right now , '' she said .

Trinite is the only hospital open in Port-au-Prince , the group said . The other two , General Hospital and Hospital de la Paix , are closed by strikes .

The school is in an extremely poor part of town , and the roads are nearly impassable , local journalist Clarens Renois said .

A United Nations helicopter was unable to land , Renois said .

`` The school is poorly built , '' said Amelia Shaw , a journalist with United Nations TV who visited the scene .

Renois described the building as `` not quite solid '' with `` weak construction . ''

The school consisted of two floors with an addition built in the rear over a 200-foot ravine , Shaw said . The steep hillside , she said , is covered with shanty-like housing on both sides .

The disaster occurred when the second floor crumbled onto the first , Shaw said .

A disaster assistance response team from the U.S. Agency for International Development arrived on the scene within hours of the collapse , the agency said in a release .

After assessing the situation , USAID activated its partner the Fairfax County Urban Search and Rescue Team . That team will be composed of 38 personnel , four search-and-rescue dogs and 31,000 pounds of rescue equipment and is expected to arrive Saturday .

The Urban Search and Rescue Team will be accompanied by four additional USAID disaster experts .

U.S. Ambassador Janet Sanderson expressed her condolences , haitipressnetwork.com reported .

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NEW : At least 50 students killed , 100 injured ; toll is expected to rise

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Red Cross official says dozens of students appear to be trapped in Haiti school

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Rescue workers digging through rubble near Port-au-Prince , official says

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School could have as many as 700 people in it , rescue official says